1. Field of Use
The invention relate to a cementitious exterior stucco material and, more particularly, to a cementitious exterior stucco material that is fast setting and resistant to shrinkage and full thickness cracking.
2. Related Art
In the southwest United States, the overwhelming percentages of structures, both residential and commercial, are built utilizing a stucco exterior wall system. The two typical stucco systems which are employed include a single coat system and a three-coat system.
A “single coat” system (which is somewhat of a misnomer) consists of a waterproof underlayment, lath, and a coat of cementitious material which is typically ¾″ to ⅞″ thick, followed by a color finish coat. A three coat system consists of a waterproof underlayment, lath, a first coat of cementitious material (scratch coat), a second coat of cementitious material (brown coat), and a third or finish (sometimes a color) coat.
Typically each coat of cementitious material is cured for a number of days before subsequent cementitious material layers are applied. This extended curing period applies before the color coat of a single coat system is applied, and it applies before both the brown coat and the color coat of a three coat system. Builders typically allow one to seven days between coats before applying a subsequent coat, which forces even small applications of three-coat external stucco to span a period of fifteen days or more.
The quality control standard governing the chemical and physical requirements for the material most often utilized for the cementitious layers is one or more of the following: ASTM C 91, Standard Specification for Masonry Cement or ASTM C 1328, Standard Specification for Plastic (Stucco) Cement, Type S or Type M, a Type I or Type II/V ASTM C 150, Standard Specification for Portland Cement and an ASTM C 206, Standard Specification for Finishing Hydrated Lime or an ASTM C 207, Standard Specification for Hydrated Lime for Masonry Purposes, lime.
The ability to work and spread the cementitious material on a surface is an important trait for stucco materials. In order to obtain the proper consistency (slump), water is typically added to the cementitious materials beyond the proportions necessary for chemical hydration of the cement. The addition of water, however, acts counter to other desired physical property of the stucco system.
Disadvantages of typical cementitious materials used in external stucco wall systems include: a) a significant time delay between the application of coats to enable curing of the stucco and/or evaporation of excess water, b) the tendency of the stucco system to develop cracks from shrinkage during curing which results from the evaporation of excess water, and c) full thickness cracking resulting from incidental movement (shifting) of the structure prior to the cementitious material developing adequate strength, due in part to the extended period of time necessary for the curing and evaporation process. Also, it is often necessary to spray or mist the applied stucco with water during the curing process in order to prevent crack development during the curing process. This generally necessitates additional labor costs.
It is desirable to produce a cementitious material to be used in stucco products which can be worked and applied easily, without creating the negative characteristics associated with addition of excess water. It is desirable to reduce the application period necessary for multiple coats of stucco, such as reducing the application period of a three-coat stucco system from the current time period of approximately fifteen days, down to as little as one day. It is desirable to reduce shrinkage cracking associated with excess water which is typically added to stucco systems for workability and ease of application, while at the same time shortening the time needed to cure and thereby reducing the potential for cracking that occurs when the surface shifts before it has cured.
Various objects of the present invention, include providing a composition, that when blended to a homogenous consistency, will provide a cementitious exterior stucco material that may be applied with either mechanical technique or hand application, (either a one coat application or a traditional three-coat application), is fast setting, shrinkage crack resistant, full thickness crack resistant, of superior flexural and compressive strength, with an initial set or workable life (board life) greater than 100 minutes. One or more of these objects are achieved by using the composition disclosed and claimed below.